Reconnaissance Geologic Map of the Petersburg 8-2 Quadrangle

U.S. DEPARTMENT OF THE INTERIOR

U.S. GEOLOGICAL SURVEY

Reconnaissance Geologic Map of the Petersburg 8-2 Quadrangle,

Southeastern Alaska

B Y

David A. Brew1

Open-File Report 97-1 56-D

This report is has not been edited or reviewed for conformity with U.S. Geological Survey editorial standards or with the North American

Stratigraphic Code. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government

Research Geologist emeritus USGS, MS 904 Menlo Park, California 94025

4 RECONNAISSANCE GEOLOGIC MAP OF THE PETERSBURG B-2 QUADRANGLE, SOUTHEASTERN

ALASKA 5

By David A. Brew

INTRODUCTION

This map and its accompanying information were prepared specifically as a U.S. Geological Survey

contribution to the joint State of Alaska Division of Geological and Geophysical Surveys and the U.S.

Department of Interior Bureau of Land Management Alaska Minerals Section (Juneau, Alaska) mineral-

resource studies of part of the Petersburg, Alaska 1 :250,000-scale quadrangle. Those studies are a direct

follow-up to geological, geochemical, and geophysical studies (cited below) done in the region by the

Alaskan Branch of the U.S. Geological Survey in the 1970's and 1980's.

The geologic information presented here has been released previously in generalized form (Brew and

others, 1984); that map is based on reconnaissance field mapping and therefore the individual maps in

this series of 1:63,360-scale maps (Brew, 1997a-m; Brew and Koch, 1997) do not have the density of

field-station control, samples, or field observations that are expected in most U.S. Geological Survey

1:63,360-scale geologic maps. There are both a combined description and a combined correlation of the

map units for this whole series of maps (Brew and Grybeck, 1997).

The available information on known mineral deposits in the whole PetersburgIWrangell area was released

previously (Grybeck and others, 1984) and Brew and others (1 989, 1991). Bedrock, stream-sediment,

and other geochemical data were released and interpreted by Karl and others (1985). Karl and Koch

(1 990), Cathrall and others (1 983a-w). and Tripp and Cathrall (1 984). Aeromagnetic and

aeroradioactivity surveys information was released by the U.S. Geological Survey (1 978, 1979) and

Bouguer gravity information by Barnes and others (1989). Remotely-sensed features were described by

LeCompte (1 981 ). Burrell and others (1 982) released a preliminary bibliography of Petersburg and

Port Alexander quadrangles-related items.

Assessments of the undiscovered mineral resources for the whole PetersburgNVrangell area are also

available (Brew and others, 1989, 1991, 1996; Brew and Drinkwater, 1991 ). Some of the mineral-

resource-assessment tract information. in neighboring areas was revised by Brew and others (1996).

Brew (1993) presented a generalized view of metallogenic belts that includes this area.

Detailed information on the Late Cretaceous plutonic rocks in the Petersburg 1 :250,000-scale quadrangle

is found in Burrell (1984abc); major-element chemical and other data for the area were reported by

Douglass and others (1989), and relatively young volcanic features were described by Brew and others

(1984) and by Brew (1990). McClelland and Gehrels (1990) reinterpreted some of the geology in and

around the Duncan Canal area, which lies to the northwest of this quadrangle.

The index map on the over-size sheet shows the major geological elements of the PetersburgIWrangell

area. They are, from west to east, (1) the Alexander belt, consisting of generally unmetamorphosed

Lower Paleozoic through Upper Triassic rocks intruded by scattered mid-Cretaceous plutons, (2) the

Gravina belt, consisting of unmetamorphosed to highly metamorphosed, variably deformed Upper

Jurassic(?) through mid-Cretaceous flysch and volcanic rocks intruded by both mid- and Upper

Cretaceous plutons, and (3) the Mainland belt, consisting of metamorphic rocks intruded by Upper

Cretaceous, lower Tertiary, and mid-Tertiary plutons. Younger than almost all parts of all of these belts,

and extending from the Alexander belt across the Gravina and onto the mainland belt, is the lower to middle

Tertiary Kuiu-Etolin belt that consists largely of varied volcanic rocks, associated plutons, and minor

sedimentary rocks. The Alexander belt corresponds more or less to the Alexander terrane of Berg and

others (1978), the Gravina belt is a refined interpretation of their Gravina belt. This quadrangle

includes only rocks of the (1) Duncan Canal-Zarembo Island-Screen Islands sub-belt of the Gravina belt,

(2) Gravina belt itself, and (3) Kuiu-Etolin belt (see Correlation of Map Units diagram on the oversize

sheet).

DESCRIPTION OF MAP UNITS

[Note: All formational and descriptive map-unit names in the text of the following descriptions are set off

with quotation marks to make them easier to identify.]

C$ SURFlClAL DEPOSITS (Holocene and(or) Pleistocene)--Includes alluvium, colluvium, tidal

mudflat deposits, and some glaciofluvial deposits. The distribution of the larger areas are shown

as mapped mapped in the field, but the deposits were not been studied in detail; many small

areas are not shown.

KUIU-ETOLIN BELT

Belt informally named by Brew and others (1979), redefined by Brew and Morrell (1983), and its age

revised by Brew and others (1 985).

EXTRUSIVE AND INTRUSIVE VOLCANIC ROCKS OF KUIU-ETOLIN VOLCANIC-PLUTONIC BELT

(Quaternary and Tertiary)--Diverse volcanic rocks exposed in a broad area extending from

northeastern Kuiu southeastward through Kupreanof and Zarembo Islands; one unit mapped in

this quadrangle:

4 QTr Rhyolite, Rhyodacite, and Related Siliceous Extrusive and Intrusive Rocks--

In general, aphanitic to finely crystalline, generally quartz and feldspar porphyritic; C. I. 'C

less than 1. Locally layered, spherulitic, and(or) miarolitic; light gray on fresh surfaces;

buff, white, green lavendar, maroon, or pink where altered; generally rusty weathering.

Pyrite and zeolites common. Many exposures are texturally complicated mixtures of

discontinuous mm-scale flow layered, brecciated, spherulitic, and phenocrystic rocks.

Heterogeneous; includes lava flows, obsidian flows, lahars, welded and nonwelded ash, tuff,

and lapilli, all cut locally by porphyritic rhyolite and rhyodacite dikes. Extreme

alteration, brecciation, attitudes of layering, and abundance of dikes define vents and

domes; massive structureless isolated rhyolite bodies suggest plugs; columnar-jointed cliff

exposures in excess of 100 m thick are interpreted as cooling units. Exposed as dikes on

Red Mountain, northwestern Etolin Island, in southwestern part of this quadrangle.

INTRUSIVE GRANITIC AND OTHER ROCKS OF KUIU-ETOLIN VOLCANIC PLUTONIC BELT (Miocene

and(or) Oligocene--Preliminary K-Ar determinations of about 20-22 Ma obtained on rocks

from the "Granite of Central and Northern Etolin IslandH (Tmge) (M. A. Lanphere, U.S.

Geological Survey, written communs., 1981, 1982); preliminary descriptions given by Hunt

(1984); as mapped in this quadrangle, divided into:

Tmge Granite of Central and Northern Etolin Island-

Hornblende-biotite granite, alkali granite, quartz syenite, and alkali quartz syenite;

massive, nonfoliated; allotriomorphic to hypidiomorphic; equigranular to seriate;

medium- to coarse-grained; C.I. 01 to 07; weathers to a distinctive pale orange to white;

miarolitic cavities common, often rusty weathering; generally homogeneous at outcrop

scale. Feldspar mineralogy consists of common, but only rarely pervasive, graphic and

micrographic intergrowths of quartz and well-developed microperthitic alkali feldspar;

mafic minerals are dark brown to greenish-brown biotite and generally subordinate green

to blue-green hornblende, both of which are often partially altered to chlorite; accessories

include sphene, allanite, and locally abundant magnetite; epidote fills miarolitic cavities in

several places. Minor amounts of fine- to medium-grained, porphyritic biotite-

hornblende quartz monzonite, quartz syenite, and granite (C.I. 03-10), frequently

containing up to 10 percent rounded, very fine grained mafic (about C.I. 40) inclusions

occur, generally near the margins. Unit forms the core of the large composite pluton on

central Etolin Island, and is best exposed there along Burnett Inlet; also exposed as small

bodies on Brownson Island, near Fisherman's Chuck, in the Niblack Islands, and in

numerous small unmapped plugs and dikes within the migmatitic rocks surrounding the

core; on northern Etolin Island, it forms the pluton at Bessie Peak in the southern part of

this quadrangle. The body at Bessie Peak has a more homogeneous composition and carries

more fine-grained mafic inclusions than does the body at Burnett Inlet in the Petersburg

A-2 quadrangle (Brew, 1997a).

Tmaz Alkali Granite of Northwestern Etolin and Southeastern Zarembo Islands--

Amphibole-biotite alkali granite and subordinate granite. Massive, nonfoliated;

allotriomorphic to hypidiomorphic; equigranular to seriate, some porphyritic; medium- to

coarse-grained; C.I. averages 04; miarolitic cavities common and locally abundant; quite

homogeneous at outcrop scale, but with locally abundant hornfels inclusions. Feldspars are

perthitic alkali feldspar, a variety of exotic (and in places pervasive) graphic and

micrographic textures, and rare occurrence of plagioclase as a separate feldspar phase; the

mafic minerals are distinctive and include green, blue-green, and blue (sodic) amphibole

(hornblende to riebeckite), dark brown to reddish-brown biotite, and locally abundant

green (iron-rich) pyroxene; the mafic minerals are altered and partially replaced by

chlorite; accessories include locally abundant sphene, allanite, apatite(?), magnetite, and

minor hematite; epidote fills some miarolitic cavities. Unit on Zarembo lsland includes

minor coarse-grained, subophitic', hornblende-biotite-pyroxene diorite (C.I. 40-45) that

resembles diorites within the "Migmatitic Granitic Rocks of Central and Northern Etolin

Island" (Tmme) as well as the diorites associated with the granites of Kupreanof and Kuiu

Islands. Unit exposed in two possibly interconnected bodies at Quiet Harbor on

northwestern Etolin lsland and at Round Point on southeastern Zarembo Island, as well as in

several small plugs and dikes that invade the adjacent country rocks on Zarembo Island.

Resembles the "Granite of Central and Northern Etolin Islandu (Tmge) in composition and

texture, while the mafic mineralogy is similar to the "Alkali Granite Satellitic to Granite of

Central Etolin Islandu (Tmae) in the Petersburg A-2 quadrangle (Brew, 1 997a).

Tsh HORNFELSED SEYMOUR CANAL FORMATION ROCKS (Miocene and(or) Oligocene)-

Albite-epidote hornfels facies rocks in aureoles on Etolin lsland which generally preserve

the original protolith structures and textures as well as the metamorphic minerals related

to older Cretaceous metamorphic events. The contacts are, as described under the heading

"Metamorphosed Stephens Passage RocksH in the section on the Gravina belt, poorly defined

and the unit may not be as extensive as presently shown. Age of protoliths is Late Jurassic

to middle Cretaceous, based on on an ammonite of Albian age (D. L. Jones, U.S. Geological

Survey, written commun., 1979) collected on the northwest shore of Etolin lsland and on

obvious derivation from the "Seymour Canal FormationH (KJss). Unit is exposed in the

southern part of this quadrangle.

,. C

GRAVINA BELT

The term Gravina belt is used here to denote sedimentary and volcanic rocks of Late Jurassic and Early L

Cretaceous age (and the pre-Cenozoic granitic and other rocks intrusive into that section) in the east-

central part of the Petersburg-Wrangell map area. As used here, the term also includes rocks of

indeterminate Mesozoic age in a broad zone to the west of and adjoining the Jurassic and Cretaceous rocks.

This zone is called the "Duncan Canal-Zarembo Island-Screen Island sub-belt" and it has within it blocks

of Paleozoic and Mesozoic rocks unlike any elsewhere in the Gravina belt, but similar to some in the

Alexander belt. The Gravina belt as used here more or less corresponds to the Gravina belt as defined by

Berg and others (1978).

INTRUSIVE ROCKS OF ADMIRALTY-REVILLAGIGEDO PLUTONIC BELT AND ASSOCIATED MlGMATlTE

(Upper Cretaceous)--Belt informally named by Brew and Morrell (1983) and described by Burrell

(1 984abc); preliminary K-Ar determinations by M. A. Lanphere (written communs., 1981, 1982)

interpreted to be applicable to the whole suite, including the rocks in this quadrangle, are as follows:

Map unit General location Biotite aae Hornblende aae

Ktif unit Wrangell Is. 83.2 Ma 91.6 Ma

11 11 Mitkof Is. - 89.1 Ma

Ktef unit Zarembo Is. 90.4 Ma 93.0 Ma

Somewhat similarly dated rocks occur in correlative units to the east in the Bradfield Canal quadrangle

(R. L. Elliott and R. D. Koch, oral commun., 1982; Koch and Berg, 1996). As mapped in this

quadrangle, divided into:

Ktef Hornblende-Biotite Tonalite and Granodiorite, Quartz Monzodiorite, and Quartz Diorite--

Foliated to massive equigranular; average grain size is medium, fine-grained near some

margins; C.I. 17 to 50; light to medium gray on fresh surfaces, weathers brownish to dark

gray. Foliation varies both in direction and development: moderately developed in west to

very well developed on east side of Wrangell Island; locally semischistose and cataclastic.

Contains aplite dikes, pegmatite dikes and veins, and rounded very fine-grained hornblende

diorite inclusions. Occurs as generally concordant sills in country rock along the margin of

the body. Mineralogy includes zoned, complexly twinned plagioclase with minor alteration

to sericite; mafic minerals are biotite in much greater amounts than hornblende; subhedral

epidote; and local garnet and pyroxene. Accessory minerals are sphene, apatite, opaque

minerals and allanite. Unit differs from "Hornblende-Biotite Tonalite, Granodiorite, etc."

(Ktif) by presence of pyroxene and garnet, and biotite as the dominant mafic phase. Unit is

exposed in the southern part of this quadrangle on Etolin Island.

Ktif Hornblende-Biotite Tonalite, Granodiorite, Quartz Monzodiorite, and Quartz Diorite--

Equigranular to sparsely porphyritic, massive to weakly foliated; medium-grained; C.I. 14

to 52; light gray on fresh surfaces, weathers yellowish-gray. Rounded, elongate very fine-

grained dioritic and some ultramafic inclusions. Mineralogic features include oscillatory

zoned seriate plagioclase, both discrete and small clumps of biotite and hornblende,

subhedral epidote or clinozoisite, rare garnet, and accessory sphene, allanite, and apatite.

Plagioclase altered to sericite and mafic minerals to epidote. Unit differs from

"Hornblende-Biotite Tonalite and Granodiorite, etc." (Ktef) by lack of pyroxene and garnet

and better development of seriate plagioclase. "Hornblende-Biotite Tonalite" (Ktop) is a

porphyritic variation of this unit. Exposed on Mitkof, Zarembo, and Woronkofski lslands

(Burrell, 1984ab) in this quadrangle.

Ktop Hornblende-Biotite To'nalite--

Porphyritic, locally foliated; medium- to coarse-grained; C.I. 15 to 40; medium to dark

gray where fresh, brownish-gray where weathered; alignment of plagioclase laths defines

foliation; rare hornfels inclusions; aplitic granite dikes, pegmatite veins, and tonalite

dikes into country rock at margins produce interfingering contacts. Plagioclase porphyritic

with local reddish-brown garnet phenocrysts; garnet-rich and -poor zones locally define

layers. Mineralogic features include zoned seriate plagioclase with minor alteration to

sericite; mafic minerals mostly in clumps; epidote and zoned garnet present; accessory

sphene, apatite, and allanite, some biotite alteration to chlorite. Body on southwestern

Mitkof Island is quartz monzodiorite in composition. Unit is gradational with "Hornblende-

Biotite Tonalite, Granodiorite, etc." (Ktif), but differs in its porphyritic texture and

ubiquitous garnet. Unit differs from "Biotite-Epidote-Hornblende Quartz Monzodiorite"

(Kqop) by the dominance of biotite over hornblende, larger hornblendes with less well

developed crystal form and (locally) abundant inclusions, presence of garnet, and clumps

of mafics as opposed to discrete mafics. Unit differs from "Biotite Tonalite, Quartz Diorite

and Granodiorite" (Ktgp) exposed in other quadrangles in abundance of hornblende and a

higher color index. Exposed on Lindenberg Peninsula, Mitkof, Rynda, Kadin, Woronkofski,

and Wrangell Islands (Burrell, 1984b).

Ktoc Garnet-Biotite Tonalite and Minor .Granodiorite--

Nonfoliated, crowded-plagioclase rock; inequigranular to porphyritic; very fine- to

medium-grained; C.I. 14 to 29; medium gray where fresh; weathers light gray; forms

small elongate bodies less than 3 square km in area; also makes up one larger body on

northern Wrangell Island. Mineralogy includes reddish-brown garnet, clinozoisite (or

rarely epidote), and local muscovite. Biotite and quartz commonly interstitial to closely

spaced plagioclase laths. Unit is similar to "Biotite Tonalite, Quartz Diorite, and

Granodiorite" (Ktgp) mapped elsewhere mineralogically, but differs texturally by its finer

grain size and lack of large phenocrysts. Exposed on northern Wrangell, Mitkof,

Woronkofski and Etolin lslands (Burrell, 1984b).

!

KSOP Biotite-Epidote-Hornblende Quartz Monzodiorite-- Locally foliated; plagioclase porphyritic with medium- and coarse-grained phenocrysts to L

12 mm, fine- to medium-grained groundmass, and a C.I. range of 17 to 48; weathers

brownish-gray, gray and white where fresh; margins of bodies are commonly more mafic

and have a very fine- to fine-grained groundmass. Muscovite-biotite garnet-epidote aplite

dikes of granitic and granodioritic composition are common. Mineralogical features include

oscillatory zoned plagioclase with sericite alteration of the cores; interstitial quartz and

K-feldspar, euhedral fine-grained hornblende, minor biotite, and primary (occasionally

twinned and zoned) and secondary epidote. Unit is exposed on the Lindenberg Peninsula,

Kupreanof Island, and on southwestern Mitkof, Woronofski and northern Zarembo Islands.

Where mapped on northern Dry Island and eastern Mitkof Island, the compositions range

from quartz monzodiorite to tonalite (Burrell, 1984ab).

METAMORPHOSED STEPHENS PASSAGE GROUP ROCKS (Upper Cretaceous)-In general, these units

are associated with the Upper Cretaceous and Tertiary plutons (of the Kuiu-Etolin Belt) in the

Gravina Belt. The rocks have been rather arbitrarily assigned a Late Cretaceous age or assigned a

Tertiary age and described elsewhere as "Hornfelsed Seymour Canal Formation Rocks" (Tsh) based on

the known or inferred age of the pluton(s) nearby. This results in a potentially misleading map

pattern, however, because the metamorphic rocks adjacent to Tertiary plutons may have undergone

previous Upper Cretaceous metamorphism as well and the units that are defined by Tertiary

metamorphic effects alone are poorly delineated. The Cretaceous age assignment used here is also not

entirely satisfactory from either a field mapping or petrographic study viewpoint; this is due to both

the complexity of spatial overlapping metamorphic effects and the apparent lack of an

unmetamorphosed protolithic unit for one of the metamorphic units mapped outside of this quadrangle.

Two units are mapped in this quadrangle:

Kss Schist and Hornfels--

Greenschist and albite-epidote to hornblende-hornfels facies metamorphic rocks derived

from "Seymour Canal Formation" (KJss) rocks; original textures and structures generally

preserved; dominantly fine- to medium-grained, grayish-brown and reddish-brown

weathering and locally foliated. Commonly compositionally layered chlorite-biotite-

quartz-feldspar schist and semischist; minor phyllite; some strongly hornfelsed rocks

close to plutons; clear-cut aureoles around Upper Cretaceous plutons are (garnet-

andalusite-staurolite-) biotite-quartz-feldspar hornfels and schistose hornfels; some

calc-silicate and intermediate composition layers and lenses locally. Age of metamorphism

varies as described in headnote above; age of protolith is Late Jurassic to middle Cretaceous

based on derivation of this unit from the "Seymour Canal Formation". Exposed in northern

and northeastern part of this quadrangle.

KSP Phyl l i te - - Subgreenschist and greenschist facies metamorphic rocks inferred to be derived from fine-

grained sediments associated with the turbidites of the "Seymour Canal Formation" (KJss);

original textures and structures generally obscure; dominantly very-fine-grained, dark-

gray weathering, carbonaceous chlorite-quartz-feldspar phyllite; some interlayered

graywacke and graywacke semischist; locally extensive layers and lenses of very-fine-

grained, light- to dark-green weathering chlorite-rich phyllite interpreted to have been

metamorphosed from fine-grained volcanic sediments such as tuffs or from highly

transposed and tectonized coarser grained intermediate composition rocks. Age

interpretation is the same as that given above for the "Schist and Hornfels" (Kss). Exposed

in northeastern part of this quadrangle.

INTRUSIVE ROCKS OF KLUKWAN-DUKE PLUTONIC BELT (Cretaceous): Belt informally named by Brew

and Morrell (1983); rocks interpreted to be 100-1 10 Ma on the basis of their similarity to dated

rocks elsewhere (Lanphere and Eberlein, 1966) and on a preliminary K-Ar age of 107 Ma from the

pluton at Turn Mountain on Kupreanof Island (M. A. Lanphere, U.S. Geological Survey, oral commun.,

1983). See also Taylor and Noble (1960), Taylor (1967), and Himmelberg and Loney (1995). One

unit mapped in this quadrangle:

Khb Hornblendite--

Hornblendite and hornblende gabbro; locally compositionally layered, fine- to medium-

grained, weathers dark grayish-green to black; C.I. 70 to 100. Locally cut by granitic

rocks like those of nearby Upper Cretaceous plutons, but on Sukoi Islets appears to cut

some granitic bodies. Also exposed on northeast shore Mitkof Island, in a large body on

northwestern Kupreanof Island at Turn Mountain that is interpreted by Brew and others

(1984) to be the outer envelope of an Alaska-type mafic/ultramafic pluton (Taylor,

1967), and in this quadrangle on the southeast side Woronkofski Island, the east side of

Zarembo Island, and on islets in Zimovia Strait.

STEPHENS PASSAGE GROUP (Upper CretaceouslCenomanian to Upper Jurassic(?))--Name proposed

by Lathram and others (1965) for the "...sequence of slate, graywacke, conglomerate, and augite- - bearing volcanic flow breccia, Late Jurassic and Early Cretaceous in age, which forms a well-defined

northwest-trending belt of rocks exposed along the eastern slopes and shores of Admiralty Island...".

This sequence also occurs south and east of Admiralty lsland (Souther and others, 1979) and extends

southward into the map-area described here. Information presented by Brew and others (1984)

showed that the Group is as young as Albian or Cenomanian, i.e., late Early and early Late Cretaceous,

in this area. The "Brother's VolcanicsNl"Douglas lsland Volcanics" probably intertongue with the

"Seymour Canal FormationN, probably near the top of the latter (Loney, 1964). Cohen and Lundberg

(1993) reported on details of the "Seymour Canal FormationN north of this quadrangle. As mapped in

this quadrangle consists of:

KJsv Brothers VolcanicslDouglas Island Volcanics-Augite-bearing flows, volcanic breccia, and

intercalated tuff, volcanic graywacke, phyllite and slate.

Andesitic to probably basaltic composition; weathers dark greenish-gray, gray, and green;

generally lighter colored where fresh; relict augite phenocrysts conspicuous in most

outcrops. Probably a few thousand meters thick; individual flow or breccia units as much

as a few hundred meters thick and graywacke, tuff, and slate lenses may also be that thick.

No fossils have been found in this unit in the Petersburg-Wrangell map area; its age is

based on its close association with the locally fossiliferous "Seymour Canal FormationN. The

"Brothers Volcanicsw named by Loney (1964) from exposures just north of this map area;

the "Douglas lsland Volcanics" named by Lathram and others(1965) on Admiralty lsland

from exposures on Douglas lsland to the north. Exposed in the eastern part of this

quadrangle on Etolin Island; the best and least deformed or metamorphosed outcrops are on

southwestern Mitkof lsland and near Steamer Bay on Etolin Island. See also Berg and others

(1 972); Ford and Brew (1977, 1978) and Page and others (1977).

KJss Seymour Canal Formation--Graywacke, slate, and minor conglomerate.

Composed largely of volcanic debris, except for the conglomerates, which are polymictic

and contain granitic clasts; most are turbidites, but nothing more is known of the

depositional environment. Weathers dark greenish-gray, brownish gray, and very dark

gray; graywacke and slatelargillite are locally calcareous and lighter colored; sedimentary

structures common, although few directional features have been noted. Probably a few

thousand meters thick; some individual graywacke units are massive and 10's of meters

thick, but most are 1 to 20 cm thick. Numerous fossil collections by Loney (1964)

established a Late Jurassic and Early Cretaceous age for the unit on Admiralty Island; that

age has been confirmed by subsequent collections (Berg and others, 1972), who collected

an Albian ammonite, a Valanginian(?) pelecypod, and Berriasian pelecypods from the

western Etolin lsland area and by collections made by Brew and others (1984), including

an Albian or Cenomanian ammonite (D. L. Jones and J. W. Miller, U.S. Geological Survey,

written commun., 1979) from hornfelsed "Seymour Canal Formationw and by

Kimmeridgian to Tithonian pelecypods from the western Etolin lsland area (R. W. Imlay,

written commun., 1982). The "Seymour Canal FormationN was named by Loney (1964)

from exposures at the mouth of Seymour Canal on Admiralty Island; the name was extended

to the rest of Admiralty lsland by Lathram and others (1965) and to northern Kupreanof

lsland by Muffler (1967). Probably grades into the more deformed and generally finer

grained "Semischist and Phyllite, Etc." (Mzs) and the "Phyllite and Slate, Etc." (M-rp) to

the west. Exposed in the northwestern part of this quadrangle.

DUNCAN CANAL-ZAREMBO ISLAND-SCREEN ISLAND SUB-BELT OF THE GRAVINA BELT

See "Gravina belt" heading (above) for background information.

METAMORPHOSED STEPHENS PASSAGE GROUP AND OTHER ROCKS (Upper(?) Mesozoic)-

Currently interpreted to be mostly metamorphic equivalents of the "Stephens Passage Group",

but in part may be derived fromw Cannery Formation" (Muffler, 1967; Brew and others,

1984), some from a different facies of the "Stephens Passage Group1', and some from a

previously unrecognized facies of Triassic rocks. As mapped in this quadrangle, includes:

Mzs Semischist and phyllite--

Metamorphosed from graywacke and siltstone: low grade (probably sub-greenschist facies) - metamorphic rocks; locally highly folded; generally poorly foliated but finer-grained

phases have good cleavage; brownish-gray where fresh, gray to brown where weathered;

relict textures and sedimentary structures indicate derivation from a graywacke and

siltstone or mudstone turbidite sequence. Unit in some places encloses several large lenses

of the "Fossiliferous Limestone" (Dls) of Devonian age, but there is no direct indication of

the age. Proximity to "Seymour Canal Formation" (KJss) outcrops and compatibility of the

protoliths with that formation suggest that this unit is a metamorphic and deformed

equivalent of that formation. Unit contrasts with the "Phyllite and Slate Metamorphosed

From Mudstone and Minor Graywacke" (Mzp) mapped elsewhere in the Petersburg-

Wrangell area in the proportion of originally coarse-grained sediments, and in the general

absence of volcanic(?) protolith phyllite in this unit. The two units probably intertongue

much more complexly than is shown on the maps. Exposed on eastern Zarembo Island in this

quadrangle.

M v Greenschist and Greenstone Metamorphosed From Intermediate to Mafic Volcanic Rocks--

Greenschist, greenstone, phyllite, minor semischist; weathers light to dark green, locally

brownish pillow breccia, agglomerate flows, and possible tuffs; appears less deformed and

less metamorphosed than other nearby rock units; probably several thousand meters thick.

Locally abundant relict pyroxene phenocrysts suggest that the protolith is the "Douglas

Island Volcanics" (KJsv). Inferred upper Mesozoic age based on association with other

units. Unit contrasts with the "Phyllite and Slate Metamorphosed From Mudstone and Minor

Graywacke" (Mp) mapped elsewhere in the Petersburg-Wrangell area in its apparent

lesser metatuff and its higher proportion of rocks of volcanic origin. Exposed along and near

Duncan Canal and on Woewodski Island, on Key Reef in Clarence Strait, and, in this

quadrangle, on Zarembo Island in the southwestern corner of the map area.

Hornblende gabbro and pyroxene-hornblende gabbro; medium to very coarse grained; C.I.

60 to 80; weathers dark greenish black and very dark green, some interstitial

indeterminate sulfide opaque minerals noted; cut by numerous dikes of medium-grained,

C.I. 05 to 25, quartz diorite like that in adjacent pluton. Crops out on east shore of Zarembo

Island.

ACKNOWLEDGEMENTS

This report could not have been produced without the efforts of my mapping colleagues, all of whom are

identified in the note on the map; the supportive and enthusiatic crew of the former U.S. Geological Survey

research vessel, the R/V Don J. Miller 11; the several helicopter pilots and mechanics who provided

efficient air transport during the field mapping; the reviewer, D.J. Grybeck, Computer Graphics

Specialist J. B. Weathers, and Illustrator Kevin Ghequiere. I thank them all.

REFERENCES CITED FOR THE PETERSBURG B-2 QUADRANGLE

Barnes, D.F., Brew, D.A., and Morin, R.L., 1989, Bouguer gravity map of the Petersburg quadrangle

and parts of the Port Alexander, Sitka, and Sumdum quadrangles, Alaska: U.S. Geological Survey

Miscellaneous Field Studies Map MF-1970-A , scale 1 :250,000, 21 p. pamphlet.

Berg, H. C., Jones, D. L., and Coney, P.J., 1978, Pre-Cenozoic tectonostratigraphic terranes of

southeastern Alaska and adjacent areas: U.S. Geological Survey Open-File Report 78-1 085, scale

1 : 1,000,000, 2 sheets.

Berg, H. C., Jones, D. L., and Richter, D. H., 1972, Gravina-Nutzotin belt--Tectonic significance of an

upper Mesozoic sedimentary and volcanic sequence in southern and southeastern Alaska, in

Geological Survey Research 1972: U.S. Geological Survey Professional Paper 800-0, p. Dl-D24.

Brew, D.A., 1990, Volcanoes of Alaska--Duncan Canal, Tlevak Strait and Suemez Island, Behm Canal

and Rudyerd Bay, in Wood, C.A., and Kienle, J., eds., Volcanoes of North America: United States

and Canada: Cambridge, University Press, p. 94-96.

1993, Regional geologic setting of mineral resources in southeastern Alaska, in Godwin, L.H., and

Smith, B. D., eds., Economic mineral resources of the Annette Islands Reserve, Alaska: U.S. Dept. of

the Interior, Bureau of Indian Affairs, Division of Energy and Mineral Resources Publication, p.

13 -20 .

1997a, Reconnaissance geologic map of the Petersburg A-2 quadrangle, southeastern Alaska: U.S.

Geological Survey Open-File Report 97-1 56-A, scale 1 :63,360, one sheet, 20 p. pamphlet.

1997b, Reconnaissance geologic map of the Petersburg A-3 quadrangle, southeastern Alaska: U.S.

Geological Survey Open-File Report 97-1 56-8, scale 1 :63,360, one sheet, 24 p. pamphlet.

1997c, Reconnaissance geologic map of the Petersburg B-1 quadrangle, southeastern Alaska: U.S.

G,eological Survey Open-File Report 97-156-C, scale 1 :63,360, one sheet, 20 p. pamphlet.

1997d, Reconnaissance geologic map of the Petersburg 8-2 quadrangle, southeastern Alaska: U.S.

Geological Survey Open-File Report 97-1 56-D, scale 1 :63,360, one sheet, 21 p. pamphlet. (This

report)

1997e, Reconnaissance geologic map of the Petersburg 8-3 quadrangle, southeastern Alaska: U.S.

Geological Survey Open-File Report 97-1 56-E, scale 1 :63,360, one sheet, - p. pamphlet.

19971, Reconnaissance geologic map of the Petersburg 8-4 quadrangle, southeastern Alaska: U.S.

Geological Survey Open-File Report 97-156-F, scale 1:63,360, one sheet, - p. pamphlet.

19979, Reconnaissance geologic map of the Petersburg B-5 quadrangle, southeastern Alaska: U.S.

Geological Survey Open-File Report 97-1 56-G scale 1 :63,360, one sheet, - p. pamphlet.

1997h, Reconnaissance geologic map of the Petersburg C-1 quadrangle, southeastern Alaska: U.S.

Geological Survey Open-File Report 97-156-H, scale 1:63,360, one sheet, - p. pamphlet.

1997i, Reconnaissance geologic map of the Petersburg C-3 quadrangle, southeastern Alaska: U.S.

Geological Survey Open-File Report 97-156-1, scale 1:63,360, one sheet, - p. pamphlet.

1997j, Reconnaissance geologic map of the Petersburg C-4 quadrangle, southeastern Alaska: U.S.

Geological Survey Open-File Report 97-156-J, scale 1:63,360, one sheet, - p. pamphlet.

1997k, Reconnaissance geologic map of the Petersburg C-5 quadrangle, southeastern Alaska: U.S.

Geological Survey Open-File Report 97-156-K, scale 1:63,360, one sheet, - p. pamphlet.

19971, Reconnaissance geologic map of the Petersburg D-4 quadrangle, southeastern Alaska: U.S.

Geological Survey Open-File Report 97-156-L, scale 1:63,360, one sheet, - p. pamphlet.

1997m, Reconnaissance geologic map of the Petersburg D-5 quadrangle, southeastern Alaska: U.S.

Geological Survey Open-File Report 97-1 56-M, scale 1 :63,360, one sheet, - p. pamphlet.

Brew, D. A., Berg, H. C., Morrell, R. P., Sonnevil, R. S., and Hunt, S. J., 1979, The mid-Tertiary Kuiu-

Etolin volcanic-plutonic belt, southeastern Alaska, in Johnson, K. M., and Williams, J. R., eds.,

The United States Geological Survey in Alaska: Accomplishments during 1978: U.S. Geological

Survey Circular 804-B, p. B129-B130.

Brew, D.A., Drew, L.J., Schmidt, L.M., Root, D.H., and Huber, D.F, 1991, Undiscovered locatable

mineral resources of the Tongass National Forest and adjacent areas, southeastern Alaska: U.S.

Geological Survey Open-File Report 91-1 0, 370 p., 15 maps at 1 :250,000, 1 map at

1:500,000, 11 figs.

Brew, D.A., and Drinkwater, J.L., 1991, Tongass Timber Reform Act Wilderness Areas supplement to

U.S. Geological Survey Open-File Report 9 1 -1 0 (Undiscovered locatable mineral resources of

the Tongass National Forest and adjacent lands, southeastern Alaska): U.S. Geological Survey

Open-File Report 91-343: 56 p.

*

Brew, D.A., and Grybeck, D.J., 1997, Combined description of map units and correlation of map units

for the Petersburg-Wrangell area 1 :63,360-scale geologic maps, southeastern Alaska: U.S.

Geological Survey Open-File Report 97-1 56-0, - p.

Brew, D.A., Grybeck, D.J., Cathrall, J.B., Karl, S.M., Koch, R.D., Barnes, D.F., Newberry, R.J.,

Griscom, A., and Berg, H.C., 1989, Mineral-resource map of the Petersburg and parts of the

Port Alexander and Sumdum 1 :250,000 quadrangles, southeastern Alaska: U.S. Geological

Survey MF-1970-B, scale 1 :250,000, 1 sheet, 47 p. pamphlet.

Brew, D.A, Grybeck, D.J., Taylor, C.D., Jachens, R.C., Cox, D.P., Barnes, D.F., Koch, R.D., Morin, R.L.,

and Drinkwater, J. L., , 1996, Undiscovered mineral resources of southeastern Alaska--Revised

mineral-resource-assessment-tract descriptions: U.S. Geological Survey Open-File Report 96-

71 6, 131 p.; one map, scale 1 :1,000,000.

Brew, D.A., Karl, S.M., and Tobey, E.F., 1985, Re-interpretation of age of Kuiu-Etolin belt volcanic

rocks, Kupreanof Island, southeastern Alaska, in Bartsch-Winkler, S., ed., The U.S. Geological

Survey in Alaska: Accomplishments during 1983: U.S. Geological Survey Circular 945, p. 86-

8 8.

Brew, D.A., and Koch, R.D., 1997, Reconnaissance geologic map of the Bradfield Canal B-6 quadrangle,

southeastern Alaska: U.S. Geological Survey Open-File Report 97-156-N, scale 1:63,360, one

sheet, - p. pamphlet.

Brew, D.A., and Morrell, R.M., 1983, Intrusive rocks and plutonic belts in southeastern Alaska, in

Roddick, J. A., ed., Circum-Pacific plutonic terranes: Geological Society of America Memoir 159,

p. 171-1 93.

Brew, D.A., Ovenshine, A.T., Karl, S.M., and Hunt, S.J., 1984, Preliminary reconnaissance geologic

map of the Petersburg and parts of the Port Alexander and Sumdum 1:250,000 quadrangles,

southeastern Alaska: U.S. Geological Survey Open-File Report 84-405, 2 sheets, 43 p.

pamphlet.

Burrell, P. D., 1984a, Map and table describing the Admiralty-Revillagedo intrusive belt plutons in the

Petersburg 1:250,000 quadrangle, Alaska: U.S. Geological Survey Open-File Report 84-171, scale

1:250,000, 6 p. pamphlet.

Burrell, P.D., 1984b, Cretaceous plutonic rocks, Mitkof and Kupreanof Islands, Petersburg

quadrangle, southeastern Alaska, in Coonrad, W.L., and Elliott, R.L., eds., The United States

Geological Survey in Alaska: Accomplishments during 1 981 : U.S. Geological Survey Circular

Burrell, P.D., 1984c, Late Cretaceous plutonic rocks, Petersburg quadrangle, southeastern Alaska, in

Reed, K.M., and Bartsch-Winkler, eds., The United States Geological Survey in Alaska:

Accomplishments during 1982: U.S. Geological Survey Circular 939, p. 93-96.

Burrell, P.D., Cobb, E.H., and Brew, D.A., 1982, Geologic bibliography of the Petersburg project area,

Alaska: U.S. Geological Survey Open-File Report 82-483, 30 p.

Cathrall, J.B., Day, G.W., Hoffman, J.D., and McDanal, S.K., 1983a, A listing and statistical summary of

analytical results for pebbles, stream sediments, and heavy-mineral concentrates from stream

sediments, Petersburg area, southeast Alaska: U.S. Geological Survey Open-File Report 83-420-A,

48p., I sheet, scale 1:250,000.

1983b, Distribution and abundance of copper, determined by spectrographic analysis, in the

minus-80-mesh fraction of stream sediments, Petersburg area, southeast Alaska: U.S. Geological

Survey Open-Fi le Report 83-420-8, 1 sheet, scale 1:250,000.

1 983c, Distribution and abundance of copper, determined by spectrographic analysis, ' in the

nonmagnetic fraction of heavy- mineral concentrates from stream sediments, Petersburg area,

southeast Alaska: U.S. Geological Survey Open-File Report 83-420-C, 1 sheet, scale 1:250,000.

1983d, '~istribution and abundance of lead, determined by spectrographic analysis, in the minus-

80-mesh fraction of stream sediments, Petersburg area, southeast Alaska: U.S. Geological Survey

Open-File Report 83-420-D, 1 sheet, scale 1:250,000.

1983e, Distribution and abundance of lead, determined by spectrographic analysis, in the


southeast Alaska: U.S. Geological Survey Open-File Report 83-420-E, 1 sheet, scale 1:250,000.

19831, Distribution and abundance of zinc, determined by spectrographic analysis, in the minus-


Open-File Report 83-420-F, 1 sheet, scale 1:250,000.

19839, Distribution and abundance of zinc, determined by spectrographic analysis, in the


southeast Alaska: U.S. Geological Survey Open-File Report 83-420-G, 1 sheet, scale 1:250,000.

1983h, Distribution and abundance of barium, determined by spectrographic analysis, in the


Survey Open-File Report 83-420-H, 1 sheet, scale 1:250,000. 1 7

1 9831, Distribution and abundance of barium, determined by spectrographic analysis, in the f


southeast Alaska: U.S. Geological Survey Open-File Report 83-420-1, 1 sheet, scale 1:250,000.

1983j, Distribution and abundance of determinable silver by spectrographic analysis, in

nonmagnetic fraction of heavy- mineral concentrates from stream sediments and in the minus- 80-

mesh fraction of stream sediments, Petersburg area, southeast Alaska: U.S. Geological Survey Open-

File Report 83-420-J, 1 sheet, scale 1:250,000.

1983k, Distribution and abundance of detectable gold, arsenic, bismuth, and antimony in the

nonmagnetic fraction of heavy- mineral concentrates and in the minus-80-mesh fraction from

stream sediments, Petersburg area, southeast Alaska: U.S. Geological Survey Open-File Report 83-

420-K, 1 sheet, scale 1:250,000.

19831, Distribution and abundance of tin, determined by spectrographic analysis, in nonmagnetic

fraction of heavy-mineral concentrates from stream sediments, Petersburg area, southeast Alaska:

U.S. Geological Survey Open File Report 83-420-L, 1 sheet, scale 1:250,000.

1983m, Distribution and abundance of cadmium, determined by spectrographic analysis, in


southeast Alaska: U.S. Geological Survey Open-File Report 83-420-M, 1 sheet, scale 1:250,000.

1 983n, Distribution and abundance of molybdenum, determined by spectrographic analysis, in the

minus-80-mesh fraction of of stream sediments, Petersburg area, southeast Alaska: U.S. Geological

Survey Open-File Report 83-420-N, 1 sheet, scale 1:250,000.

1 9830, Distribution and abundance of molybdenum, determined by spectrographic analysis, in

nonmagnetic fraction of heavy- mineral concentrates from stream sediments, Petersburg

area,southeast Alaska: U.S. Geological Survey Open-File Report 83-420-0, 1 sheet, scale

1:250,000.

1983p, Distribution and abundance of nickel, determined by spectrographic analysis, in the

minus-80-mesh fraction of stream sediments from the Petersburg area, southeast Alaska: U.S.

Geological Survey Open-File Report 83-420-P, 1 sheet, scale 1:250,000.

1983q, Distribution and abundance of nickel, determined by spectrographic analysis, in


southeast Alaska: U.S. Geological Survey Open-File Report 83- 420-Q, 1 sheet, scale 1:250,000.

1983r, Distribution and abundance of cobalt, determined by spectrographic analysis, in the minus-


Open-File Report 83-42043, 1 sheet, scale 1:250,000.

1983s, Distribution and abundance of cobalt, determined by spectrographic analysis, in the


southeast Alaska: U.S. Geological Survey Open-File Report 83-420-S, 1 sheet, scale 1:250,000.

1983t, Distribution and abundance of chromium, as determined by spectrographic analysis, in the


Survey Open-File Report 83-420-T, 1 sheet, scale 1:250,000.

1983u, Distribution and abundance of chromium, as determined by spectrographic analysis, in the

nonmagnetic fraction of heavy-mineral concentrates from stream sediments, Petersburg area,

southeast Alaska: U.S. Geological Survey Open-File Report 83-420-U, 1 sheet, scale 1:250,000.

1983v, Distribution and abundance of tungsten, determined from colorimetric and spectrographic

analysis, in the minus- 80-mesh fraction of stream sediments, Petersburg area, southeast Alaska:

U .S. Geological Survey Open-File Report 83-420-V, 1 sheet, scale 1:250,000.

1983w, Distribution and abundance of tungsten, determined by spectrographic analysis, in


southeast Alaska: U.S. Geological Survey Open-File Report 83-420-W, 1 sheet, scale 1:250,000.

Cohen, H.A., and Lundberg, N., 1993, Detrital record of the Gravina arc, southeastern Alaska: Petrology

and provenance of Seymour Canal Formation sandstones: Geological Society of America Bulletin, v.

105, p. 1400-1414.

Douglass, S.L., Webster, J.H., Burrell, P.D., Lanphere, M.L., and Brew, D.A., 1989, Major element

chemistry, radiometric values, and locations of samples from the Petersburg and parts of the

Port Alexander and Sumdum quadrangles, southeastern Alaska: U.S. Geological Survey Open-File

Report 89-527, map at 1: 250,000, 66 p. pamphlet.

Ford, A. B., and Brew, D. A., 1977, Chemical nature of Cretaceous greenstone near Juneau, Alaska, in

Blean, K. M., ed., The United States Geological Survey in Alaska: Accomplishments during 1976:

U.S. Geological Survey Circular 751 -8, p. 888-890.

1978, Minor metal content of Cretaceous greenstone near Juneau, Alaska, in Albert, N. R. D., and

Hudson, Travis, eds., The United States Geological Survey in Alaska: Accomplishments during

1979: U.S. Geological Survey Circular 823-8, p. 899-8101. 1 9

Grybeck, D.J., Berg, H.C., and Karl, S.M., 1984, Map and description of the mineral deposits in the I

Petersburg and eastern Port Alexander quadrangles, southeastern Alaska: U.S. Geological Survey

Open-File Report 84-837, scale 1:250,000, 87 p. pamphlet.

Himmelberg, G.R., and Loney, R.A., 1995, Characteristics and petrogenesis of Alaskan-type ultramafic-

mafic intrusions, southeastern Alaska: U.S. Geological Survey Professional Paper 1564, 47 p.

Hunt, S. J., 1984, Preliminary study of a zoned leucocratic granite body on central Etolin Island,

southeast Alaska, in Coonrad, W. C., and Elliott, R.L., eds., The United States Geological Survey in

Alaska: Accomplishments during 1981 : U.S. Geological Survey Circular 868, p. 128-1 31.

Karl, S.M., Koch, R.D., Hoffman, J.D., Day, G.W., Sutley, S.J., and McDanal, S.K., 1985, Trace element

data for rock samples from the Petersburg, and parts of the Port Alexander and Sumdum

quadrangles, southeastern Alaska: U.S. Geological Survey Open-File Report 85-1 46, scale

1 :250,000, 698 p.

Karl, S.M., and Koch, R.D., 1990, Maps and preliminary interpretation of anomalous rock geochemical

data from the Petersburg quadrangle and parts of the Port Alexander, Sitka, and Sumdum

quadrangles, southeastern Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF

1970-C, 40 p. pamphlet, 7 sheets.

Koch, R.D., and Berg, H.C., 1996, Reconnaissance geologic map of the Bradfield Canal quadrangle,

southeastern Alaska: U.S. Geological Survey Open-File Report 81-728-A, scale 1 :250,000, 35 p.

pamphlet.

Lathram, E. H., Pomeroy, J. S., Berg, H. C., and Loney, R. A., 1965, Reconnaissance geology of Admiralty

Island, Alaska: U.S.Geological Survey Bulletin 1 181 -R, p. B1-R48, 2 pls., scale 1 :250,000.

LeCompte, J.R., 1981, Landsat features maps of the Petersburg quadrangle and vicinity, southeastern

Alaska: U.S. Geological Survey Open-File Report 81-799, 2 sheets, scale 1:250,000.

Loney, R. A., 1964, Stratigraphy and petrography of the Pybus-Gambier area, Admiralty Island, Alaska:

U.S. Geological Survey Bulletin 1 178, 103 p.

McClelland, W. C., and Gehrels, G.E., 1990, Geology of the Duncan Canal shear zone: Evidence for Early-

Middle Jurassic deformation of the Alexander terrane, southeastern Alaska: Geological Society of

America Bulletin, v. 102, p. 1378-1392.

Muffler, L. J. P., 1967, Stratigraphy of the Keku Islets and neighboring parts of Kuiu and Kupreanof

Islands, southeastern Alaska: U.S. Geological Survey Bulletin 1241 -C, p. C1 -C52.

Page, N. J., Berg, H. C., and Haffty, J., 1977, Platinum, palladium, and rhodium in volcanic and plutonic

rocks from the Gravina-Nutzotin belt, Alaska: U.S. Geological Survey Journal of Research, v. 5, p.

629-636.

Taylor, H. P., 1967, The zoned ultramafic complexes of southeastern Alaska, in Wyllie, P. J., ed.,

Ultramafic and related rocks: J. Wiley and Sons, p. 97-121.

Taylor, H. P., Jr., and Noble, J. A., 1960, Origin of the ultramafic complexes in southeastern Alaska:

International Geological Congress, 21st, Copenhagen 1960, pt. 13, p. 175-187.

Tripp, R.B., and Cathrall, J.B., 1984, Mineralogical map showing the distribution of selected minerals in

nonmagnetic fraction of heavy-mineral concentrates from stream sediments, Petersburg area,

southeast Alaska: U.S. Geological Survey Open-File Report 83-420-X, 1 sheet, scale 1:250,000.

Souther, J. G., Brew, D. A., and Okulitch, A. V., 1979, Sheet 104-1 14, lskut River, British Columbia-

Alaska: Geological Survey of Canada, Geological Atlas Map 1418A, 3 sheets, scale 1 :I ,000,000.

U.S. Geological Survey, 1978, Aeroradioactivity of Kosciusko Island, Alaska: U.S. Geological Survey Open-

File Report 79-831, 1 sheet, scale 1:63,360.

1979, Aeromagnetic map of Petersburg area, Alaska: U.S. Geological Survey Open-File Report 79-

832, 1 sheet, scale 1:250,000.

Documents

Reconnaissance Geologic Map of the Petersburg 8-2 Quadrangle